An organ culture technique approximating in utero conditions will be used to provide a model of palatal shelf elevation and fusion which will permit direct study of the nature and interplay of the forces involved in these processes. Intact and partially dissected embryonic mouse heads will be cultured from the earliest stage of palatal shelf formation through the stages of elevation and closure. This technique allows shelves to develop in a normal relationship to other oral structures. Heads are mounted so that the shelves must counteract gravity forces to effect closure. The system will be used to better define the occurrence and timing of cellular events involved in palatal closure. Direct experimental manipulation of the craniofacial complex will be used to study the role of the tongue, mandible, brain, cranial base and the shelves themselves in the closure process. Cultured preparations will be compared to an in vivo series of embryos histologically and in terms of both 3H-thymidine and 35S-sulfate uptake in various regions of the craniofacial complex. Pulse labeling of the culture medium will permit fine dissection of the time course of these events during shelf closure. Agents with specific effects on cell processes (e.g., actinomycin D, puromycin, colchicine, cytochalasin B, hyaluronidase) will be administered both in the culture medium and by microinjection into local regions of the craniofacial area. Their effects on palatal closure will be evaluated morphologically and histologically. The role of cell migrations in shelf elevation will be examined using cytochalasin B, microinjection of vital dyes, and implantation of very small amounts of H3-thymidine labeled tissue. The dispersion of labeled cells will be followed by direct observation and autoradiography. Teratogens known to induce cleft palate, e.g., cortisone and diphenylhydantoin, will also be administered in the culture medium and by microinjection to determine their time of action and effects on craniofacial structures alone.